| 摘要 |
PROBLEM TO BE SOLVED: To make the diameter of pores larger, and increase the permeability by a method wherein a solution is prepared by respectively adding specified amounts of a polyolefin composition wherein the weight average molecular weight, etc., are specified, and a solvent, and this solution is extruded from a die, and the cooling condition when a film is formed by drawing by a cooling roll, is specified. SOLUTION: A solution of 5-40 wt.% of a polyolefin composition, which is a mixture of an ultra-high molecular weight polyolefin A, of which the weight average molecular weight is 5×10<5> or higher, and polyolefin B of which the weight average molecular weight is less than 5×10<5> , and wherein the weight ratio of B/A is 0.2-20, and 95-60 wt.% of a solvent, is extruded from a die, and drawn by a cooling roll, and a film is formed. In this case, an interval between the die and the cooling roll is made 5-100 mm, the temperature of the cooling roll is made 30-100 deg.C (the crystallization temperature of polyolefin), and the take-off speed is made 1-20 m/min. Then, it is washed with a solvent, and the residual solvent is removed. As a result, a high permeable film of which the air permeability is 5-100 sec/100cc, of which the void content is 35-05%, and of which the average through hole diameter is 0.05-1.0μm, is obtained. |
